multimode distortion

In an optical waveguide, – typically a multimode fiber - the distortion resulting from differential mode delay, i.e. axial rays (modes), with the shortest path length, will have the shortest transmission time, while rays entering the fiber at its maximum acceptance angle will travel farther and require the maximum time. This results in the original source signal being spread in time because the on and off axis modes do not propagate in sync and do not reach the detector in unison.